Sealing and desmudging anodized aluminum

ABSTRACT

TRIETHANOLAMINE SEALING OF ANODIZED ALUMINUM FOLLOWED BY DESMUDGING WITH ONE OR MORE MINERAL ACIDS.

United States Patent Office 3,822,156 Patented July 2, 1974 3,822,156 SEALING AND DESMUDGING ANODIZED ALUMINUM Paul F. Wallace, New Kensington, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa. N Drawing. Filed Jan. 12, 1973, Ser. No. 323,327

Int. Cl. C23f 1/00 US. Cl. 156-22 7 Claims ABSTRACT OF THE DISCLOSURE Triethanolamine sealing of anodized aluminum followed by desmudging with one or more mineral acids.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to sealing of aluminum having an anodic coating thereon. More particularly, it relates to sealing and desmudging of anodized aluminum. By aluminum I mean aluminum and aluminum base alloys containing at least 50% by weight aluminum.

2. Description of the Prior Art Elimination of smudge formed on anodized aluminum during sealing still presents a problem in the aluminum industry, particularly in the architectural and automotive fields. Attempts have been made both to prevent formation of the smudge and to remove it after it is formed, neither with 100% success. For example, various additives such as surfactants have met with only limited success in attempts to minimize smudge creation during sealing with hot water or aqueous solutions of compounds such as nickel or cobalt acetate, ammonium acetate, sodium or calcium sulfate or phosphate and the like. Also, attempts to remove smudge unavoidably formed during such sealing, for example, by treatment with mineral acids, have also not always been entirely satisfactory, particularly in that, while in some instances reasonable amounts of smudge have been removed in this manner, sometimes smudge removal has been incomplete, and, on other occasions, employing the smudge removal step has been detrimental to the degree and quality of the seal. Accordingly, finding how to efficiently prevent a smudge problem represents a highly desirable result.

SUMMARY OF THE INVENTION After extended investigation I have found that smudge can be elliciently removed from anodized aluminum without detrimentally affecting the seal by sealing the anodized aluminum in a solution of triethanolamine in hot water, preferably at a temperature of from about 175 F. to about 212 F., the optimum being near the boiling point range for the solution, or from about 185 F. to about 212 F., and thereafter desmudging with one or more mineral acids, preferably, nitric, sulfuric, hydrochloric, phosphoric or the like. Best sealing according to the invention takes from about minutes to about 30 minutes depending upon the coating, the best desmudging takes from about 1 minute to about 20 minutes. While even the smallest amount of triethanolamine is useful according to the invention, I have found from about 3 ml./l. to about 10 ml./l. to be most effective. The sealing solution may also contain conventional additives such as surfactants, if desired. Other than the fact that highly concentrated mineral acid solutions tend to remove some of the seal, the concentration of the desmudging acid used is not critical according to the invention. However, I have found that in my two-step sealing and desmudging process a 1:1 or greater dilution of the concentrated acid with water is preferable in the desmudging step for obtaining best results. For most efficient results the mineral acid employed in the desmudging step should be at a concentration of at least about by weight, preferably at least about by weight. Application of the acid may be by spraying, dipping or the like. The temperature of the acid employed in the desmudging step is not critical. Room temperature, for example, 65 F.- 90 F., is satisfactory. However, the acid may be heated to a higher temperature, if desired. A boiling temperature should be avoided so as to avoid removal of a substantial amount of the seal. Even cold acid at a temperature as low as around the freezing point of 32 F. effects some desmudging.

While some aluminum base alloys may be desmudged somewhat more efliciently then others according to the invention, in general, the alloy treated makes little difference.

The anodized aluminum to be sealed and desmudged according to the invention may be formed by any conventional method. For example, the anodic coating on the aluminum may be created by anodizing (passing electric current through the treating solution with the object being coated serving as anode) in a sulfuric acid solution or a sulfuric acid containing sulfophthalic acid solution, for example, according to well known procedures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples are illustrative of the invention.

Example 1 The following table compares sealing and desmudging results of representative prior art treatments with the TABLE Dissolution,

Before After Loss, 5', Effectiveness of HNO;

Seal bath sealing sealing gain HNOs desmudged (visual) min. boiling seals D.I. H2O 6.0 5. 2 2. 34 0. 24 Not completely desmudged- 0. 47 0. 66 1 ml./l. TE 8.0 7. 8 1. 86 1. 01 Desmudged completely. O. 36 0. 50 5 ml./l. TEA. 8. 2 8. 1 1. 56 2. d 0.17 0. 25 10 mL/l. TEA 8.2 8.1 1. 13 5. 0.11 0.20 0.5 gm./l. NlAc 6. 2 6. 1 2. 98 0. l. 05 0.43 5.0 gm./l. NiAc.... 6. 3 6. 1 4. 40 3. 46 Desmudged completely. 0. 42 0. 42

10 min. boiling seals 3. 9 4. 2 1. 80 0. 05 Not completely desmudged. 1. 57 2. 33 8. 1 8. 3 1. 76 1. 04 Desmudged completely. 0. 42 0.61 8.7 8.8 1.42 2.13 o 0.31 0.33 8. 3 8. 5 1. 50 1. 0. 40 0.32 7. 5 6. 2 4. 26 3. 37 0. 52 0. 48

1 Delonlzed. l 'Irlethanolamine. 8 Acetate.

results of triethanolamine sealing and mineral acid desmudging (here a minute desmudging treatment with HNO 1:1 by volume). The product treated in each instance was anodized sheet of 1100 aluminum (Aluminum Association designation for aluminum of 99.00 percent minimum purity alloyed with 0.12 Cu). In each instance the desmudging step followed the sealing step and was at room temperature of 75 F. The weight loss or acid dissolution test was employed to determine the efiiciency of the seal, the lower the value in mg./in. the better the seal. This includes, after acid desmudging, checking the weight loss (mg/in?) upon treatment with chromic/phosphoric acid. Two separate minute period dissolution treatments were used as a double check. The table also shows the results of measurements made to determine Weight gain in the sealing step and weight loss in the desmudging step.

Example 2 Sulfuric, phosphoric and hydrochloric acids in respective concentrations by weight of and may be used in the desmudging step after sealing samples of anodized 1100 aluminum alloy (e.g. anodized 35 minutes in a sulfuric acid/sulfophthalic acid electrolyte at F. and 24 asf) with a water solution containing 5 ml./l. triethanolamine at about F. Smudge formed during the sealing step can be substantially removed in each instance with no apparent damage to the seal.

Example 3 Successive sealing and desmudging steps substantially as in Example 2 except for the sealing step being conducted at 208 F. at a pH of 8.5 for 20 minutes and the desmudging being for 2 minutes may be employed on other aluminum base alloys, including those containing, for example, Zn, Mg and Cu as modifying elements, and, specifically, an aluminum base alloy containing in percent by weight 0.5 Cu, 0.18 Fe, 0.10 Si, 0.01 Mn, 0.04 Mg, 0.18 Cr and 0.02 Ti with equally good desmudging results and without the seal being detrimentally affected.

While the invention has been described in terms of preferred embodiments, the claims appended hereto are intended to encompass all embodiments which fall within the spirit of the invention.

Having thus described my invention and certain preferred embodiments thereof, I claim:

1. A process for improving smudge removal without adversely affecting seal quality of anodized aluminum which comprises sealing anodized aluminum in a hot aqueous solution of triethanolamine and thereafter removing smudge formed on said anodized aluminum during said sealing by treating the sealed anodized aluminum with a mineral acid.

2. The process of Claim 1 wherein the mineral acid is selected from the group consisting of nitric, hydrochloric, sulfuric and phosphoric.

3. The process of Claim 1 wherein the aqueous solution of triethanolamine comprises at least about 3 milliliter per liter of water.

4. The process of Claim 1 wherein the aqueous solution of triethanolamine comprises from about 3 milliliter per liter of water to about 10 ml. per liter of water.

5. The process of Claim 1 wherein the treating with a mineral acid is for from about 1 minute to about 20 minutes.

6. The process of Claim 1 wherein the mineral acid is nitric.

7. A process for improving the efiiciency of sealing and desmudging aluminum which comprises sealing anodized aluminum in a boiling solution of from about 3 milliliter to about 10 milliliters of triethanolamine in water for from about 5 minutes to about 30 minutes, thereupon forming smudge on said anodized aluminum, and thereafter removing smudge from the sealed anodized aluminum by treating same from about 1 minute to about 20 minutes with at least one mineral acid selected from the group consisting of nitric, phosphoric, sulfuric and hydrochloric at a concentration of at least about 20% by weight.

References Cited UNITED STATES PATENTS 2,472,304 6/1949 Mason l5622 X 3,016,293 1/1962 Cybiwsky et a1. l5622X 3,123,503 3/1964 I-Iumphreys l5622 X WILLIAM A. POWELL, Primary Examiner US. Cl. X.R. 

